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DEE-24106 ELECTRIC POWER SYSTEMS

Enrigue Acha and Sami Repo
11th of April, 2016

Attempt ALL guestions

The numbers in sguare brackets in the right-hand margin indicate the marks allotted to the
part of the guestion against which the mark is shown. These marks are for guidance only.

An electronic calculator may be used provided that it does not have a facility for either
textual storage or display, or for graphical display.
If a calculator is used, intermediate steps in the calculation should be indicated.

Ol (a) State briefly what is the main objective of a conventional power flow study. [1]

(b) State the three types of nodes used in a conventional power flow solution, the
two specified variables and the two calculated variables associated with each
type of node. [1]

(b) For the circuit shown in Fig. 1 determine the nodal voltage solution using one
iteration of the power flow Newton-Raphson method. Select bus 1 to be the
slack bus, with a voltage magnitude of 1.05 p.u. and 0 phase angle. The
voltage magnitudes at buses 2 and 3 are kept at 1 p.u. each. To start the
iterative solution, assume 0 phase angles in buses 2 and 3. [4]

P1,=0.5p.v.
0,20 p.u.

  
 
   
   

4
Paz=0.2p.u.
02 — The power circuit shown in Fig. 2 undergoes a two-phase short-circuit fault in
bus 3.

(a) Calculate the short-circuit fault currents (positive and negative) assuming a
flat voltage profile of 1 p.u. in all buses just before the fault occurs and zero

fault impedance, i.e. Z;= 0+j0. [3]

(b) Determine the faulted nodal voltages in all five buses, in seguence guantities.[3]

JXa5j0.1 p.v. X 5j0.1 p.u. JÄ j0.1 pu.
JX0j0.1 puu. jXo 5j0.1 p.u. X5j0.1 p.u.

  
   

X 0.1 p.u. JÄ jo.1 pv.

X07j0.05 p.u. 1X05j0.05 p.u.
JAG j0.1 p.u. jX/y =j0.1 p.u.
jX o =j0.1 p.u. joy j0.1 p.u.

03 (a) State using your own words what is Power Ouality. HJ

(b) State using your own words what is harmonic distortion of the current and
voltage waveforms. [1]

(c) Which are the dominant harmonics produced during the normal operation of
the following eguipment: (i) a six-pulse Static Var Compensator (SVC); (ii) a
six-pulse rectifier thyristor bridge; (iii) a saturated power transformer. [3]

(d) State using your own words what is the main intended function of a filtering
system in a SVC installation. [1]

04 Write a short essay on transmission line series compensation: describe the
structure of a series compensator, the principles behind it and the main objectives
of this long-distance transmission resource. Draw necessary diagrams to explain
electrical properties of series compensation. When and how it is advisable to
employ series compensation in a transmission line? What special issues
associated with series compensation should be considered carefully at the
planning stage? [6p]

 
O5 Describe in chronological order what it is expected to happen in a well-
functioning power system, during and immediately after the sudden
disconnection of a large synchronous generator. [6p]